Field of the Invention
The present invention relates to a disclination correction performed on a liquid crystal element.
Description of the Related Art
Liquid crystal elements are used in many display apparatuses each displaying images such as direct-view monitors and liquid crystal projectors. FIG. 11 schematically illustrates a structure of a liquid crystal element. The liquid crystal element includes, between a common electrode 1001 and multiple pixel electrodes 1002, a liquid crystal layer containing liquid crystal molecules 103 (only one liquid crystal molecule is illustrated in the drawing). A voltage applied on each of the pixel electrodes 1002 (that is, a potential difference between the common electrode 1001 and that pixel electrode 1002) is changed depending on a tone of a video signal. Changing the voltage applied on the pixel electrode 1002 enables controlling a direction of the liquid crystal molecule 1003 and thereby controlling an amount of light exiting from a pixel including the liquid crystal molecule 1003 (that is, a display tone of the pixel). Controlling the directions of the liquid crystal molecules 1003 in multiple pixels on the liquid crystal element enables displaying a video image.
The direction of the liquid crystal molecule 1003 is defined by a polar angle θ and an azimuth angle ϕ in a spherical coordinate system illustrated in FIG. 11. The polar angle θ is changeable depending on the potential difference (absolute value) between the common electrode 1001 and the pixel electrode 1002. In a liquid crystal display element of a so-called normally black mode, an increase in the potential difference increases the polar angle θ and increases the display tone. On the other hand, the azimuth angle ϕ becomes a specific angle (pre-tilt azimuth angle) due to a weak alignment regulating force caused by an alignment film formed on surfaces of the common electrode 1001 and the pixel electrode 1002.
However, the liquid crystal display element has a commonly known problem, namely, disorder in alignment of the liquid crystal molecules, which is so-called disclination, and a decrease in image quality due to the disclination. FIG. 10 illustrates an example of generation of the disclination. When an image containing a white background and a black line 901 extending vertically is displayed as illustrated in FIG. 10, a dark line (disclination line) 902 due to the disclination, which is caused by a difference in potential difference (drive voltage) between mutually adjacent pixels, is generated in pixels adjacent right to pixels displaying the black line 901. Description will be made of directions of liquid crystal molecules in a pixel 900 in which the disclination is generated with referring to FIG. 9A.
In FIG. 9A, multiple liquid crystal molecules 801 contained in the pixel 900 in which the disclination is generated have a pre-tilt azimuth angle set by the alignment film formed on the surface of the electrode such that the molecules 801 are oriented in a pre-tilt direction 803 expressed by a dashed-dotted line extending in an upper left and lower right direction in the drawing. In addition, the polar angle of each liquid crystal molecule 801 that is an angle formed with respect to a normal to a plane of the drawing changes depending on the drive voltage, which provides tones from black to white. The drawing illustrates an example of a negative liquid crystal whose liquid crystal molecules 801 are oriented in a direction vertical to the plane of the drawing in a state in which the drive voltage is not applied and are oriented in a direction parallel to the plane of the drawing (and in the pre-tilt direction 803) in a state in which the drive voltage is applied. In the pixel 900, multiple liquid crystal molecules 802 located in an area adjacent to the pixel (black display pixel) displaying the black line 901 in FIG. 10 are affected by the difference in potential difference from the black display pixel and thus are oriented in a direction 804 different from the pre-tilt direction 803 (that is, a direction parallel to a vertical side of the pixel 900). Consequently, as illustrated in FIG. 10, the disclination line 902 is generated in the pixel 900.
Japanese Patent Laid-Open No. 2012-203052 discloses an image processing method of decreasing a difference in a tone level of a target pixel from that of an adjacent pixel in order to reduce the generation of the disclination in the target pixel.
In addition, a condition of the generation of the disclination depends not only on a magnitude of the difference in potential difference from the adjacent pixel, but also on a relation between a direction of a gradient of the potential difference and the pre-tilt azimuth angle. A pixel 903 illustrated in FIG. 10 is a pixel whose sign of the gradient of the potential difference with respect to the pre-tilt direction 803 is inverse to that of the pixel 900. In such a pixel 903, as illustrated in FIG. 9B, though a direction 806 of liquid crystal molecules 805 slightly changes with respect to the pre-tilt direction 803 illustrated in FIG. 9A due to an influence of the difference in potential difference from the adjacent pixel, the direction 806 does not become parallel to the vertical side of the pixel 903. For this reason, the disclination is not generated in the pixel 903.
Furthermore, displaying on the liquid crystal element a moving image constituted by continuous frame images each generating the disclination in the liquid crystal element results in a degradation in image quality that is a so-called disclination tailing. FIG. 8 illustrates a state in which a disclination tailing 703 is generated in a displayed moving image (between multiple frame images) containing a white background and a black rectangle. At a right side and a lower side of the black rectangle, disclination lines 701 and 702 are generated. When the black rectangle moves in a direction in which the disclination remains, a temporal residue of the disclination in its reducing process seems like a tail. In particular, when, as indicated by a white-filled arrow in the drawing, a movement direction of the black rectangle is an oblique direction opposite to a convex direction of a white-background side corner portion of the black rectangle (that is, an upper left oblique direction in the drawing), the disclination tailing 703 noticeably appears.
Reducing the generation of the disclination using the method disclosed in Japanese Patent Laid-Open No. 2012-203052 enables reducing the generation of the disclination tailing caused thereby. However, the disclination (namely, the disclination tailing) is likely to be generated when a temperature of the liquid crystal element is higher than a specific temperature (for example, 50° C.). In other words, the disclination tailing is not likely to be generated when the temperature of the liquid crystal element is lower than the specific temperature. Therefore, implementing the method disclosed in Japanese Patent Laid-Open No. 2012-203052 regardless of the temperature of the liquid crystal element may undesirably decrease a brightness or a contrast of a displayed image.